I am not sure if this is already published here or not, but I am not able to find it anywhere on the site so I will publish what I found out about Dashboard's drag and drop behavior. I have just discovered that you can drag files, images, attachments in Mail, and selected text from your Desktop workspace to Dashboard widgets. This is performed, for example, by dragging a file in Finder, pressing F12 (to launch Dashboard), and dropping the file onto the appropriate widget in Dashboard.

To get a really good feel for how this works, install the Framing gallery and Dropper widgets that are located in /Developer -> Examples -> Dashboard -> Sample widgets. To get these widgets, you need the Developer Tools installed on your system. If you don't have the dev tools installed, you can just download the Frameurl widget and use it instead.

My favorite example is to take an image file from Finder or an attachment, drag it, hit F12, and drop it onto the Framing Gallery widget. The Frame will adjust to the size of the image. An additional bonus is if you have an animated GIF file and you drag it to this widget, it will play! The downside is that it will only take one image at a time.

Another good example is to take an attachment from Mail, drag it, hit F12, and drop it onto the Dropper widget. The result is that you get the file/URL location of the attachment. Sure you can do this with Terminal, but you have the option of using the widget if you want to. The Dropper widget also works on a URL from a browser.

A more generic example is you can select some text from Mail, TextEdit, your browser, etc. Drag the selected text, hit F12, and drop the selected text onto any widget that will accept the text such as the Dictionary, Wikipedia or Notepad widgets. From there, you can activate the widget on the selected text as normal.

There are probably other good examples with Dashboard drag and drop behavior, but I wanted to highlight the ones that I found interesting. Please feel free to weigh in on your experience.

This is especially useful with widgets that manipulate files such as Upload to FTP (a la Transmit Widget) or other websites (flickr, etc) , Encrypt files, Erase files safely, etc

I found that this is best achieved if you have a multi button mouse where you can assign one of the lesser used buttons to bringing up the dashboard. Then the operation is almost as simple as a regular drag n drop (Click and hold file, click alternate button to bring up dashboard, and drop on selected widget)